Yang Q, Chen S-R, Li D-P, Pan H-L
Department of Anesthesiology and Pain Medicine, Unit 110, The University of Texas M. D. Anderson Cancer Center, 1515 Holcombe Boulevard, Houston, TX 77030, USA.
Neuroscience. 2007 Oct 26;149(2):315-27. doi: 10.1016/j.neuroscience.2007.08.007. Epub 2007 Aug 8.
The paraventricular nucleus (PVN) of the hypothalamus is important for the neural regulation of cardiovascular function. Nitric oxide (NO) increases synaptic GABA release to presympathetic PVN neurons through the cyclic guanosine monophosphate (cGMP)/protein kinase G signaling pathway. However, the downstream signaling mechanisms underlying the effect of NO on synaptic GABA release remain unclear. In this study, whole-cell voltage-clamp recordings were performed on retrograde-labeled spinally projecting PVN neurons in rat brain slices. Bath application of the NO precursor l-arginine or the NO donor S-nitroso-N-acetylpenicillamine (SNAP) significantly increased the frequency of GABAergic miniature inhibitory postsynaptic currents (mIPSCs) in labeled PVN neurons. A specific antagonist of cyclic ADP ribose, 8-bromo-cyclic ADP ribose (8-Br-cADPR), had no significant effect on l-arginine-induced potentiation of mIPSCs. Surprisingly, blocking of voltage-gated potassium channels (Kv) with 4-aminopyridine or alpha-dendrotoxin eliminated the effect of l-arginine on mIPSCs in all labeled PVN neurons tested. The membrane permeable cGMP analog mimicked the effect of l-arginine on mIPSCs, and this effect was blocked by alpha-dendrotoxin. Furthermore, the specific Kv channel blocker for Kv1.1 (dendrotoxin-K) or Kv1.2 (tityustoxin-Kalpha) abolished the effect of l-arginine on mIPSCs in all neurons tested. SNAP failed to inhibit the firing activity of labeled PVN neurons in the presence of dendrotoxin-K, Kalpha. Additionally, the immunoreactivity of Kv1.1 and Kv1.2 subunits was colocalized extensively with synaptophysin in the PVN. These findings suggest that NO increases GABAergic input to PVN presympathetic neurons through a downstream mechanism involving the Kv1.1 and Kv1.2 channels at the nerve terminals.
下丘脑室旁核（PVN）对心血管功能的神经调节很重要。一氧化氮（NO）通过环磷酸鸟苷（cGMP）/蛋白激酶G信号通路增加突触前PVN神经元的GABA释放。然而，NO对突触GABA释放影响的下游信号机制仍不清楚。在本研究中，对大鼠脑片逆行标记的脊髓投射PVN神经元进行全细胞膜片钳记录。浴用NO前体L-精氨酸或NO供体S-亚硝基-N-乙酰青霉胺（SNAP）显著增加标记的PVN神经元中GABA能微小抑制性突触后电流（mIPSCs）的频率。环ADP核糖的特异性拮抗剂8-溴环ADP核糖（8-Br-cADPR）对L-精氨酸诱导的mIPSCs增强无显著影响。令人惊讶的是用4-氨基吡啶或α-树眼镜蛇毒素阻断电压门控钾通道（Kv）消除了L-精氨酸对所有测试的标记PVN神经元中mIPSCs的影响。膜通透性cGMP类似物模拟了L-精氨酸对mIPSCs的影响，且这种影响被α-树眼镜蛇毒素阻断。此外，Kv1.1（树眼镜蛇毒素-K）或Kv1.2（墨西哥毒蛛毒素-Kα）的特异性Kv通道阻滞剂消除了L-精氨酸对所有测试神经元中mIPSCs的影响。在存在树眼镜蛇毒素-Kα的情况下，SNAP未能抑制标记的PVN神经元的放电活动。此外，Kv1.1和Kv1.2亚基的免疫反应性在PVN中与突触素广泛共定位。这些发现表明，NO通过涉及神经末梢Kv1.1和Kv1.2通道的下游机制增加对PVN交感神经节前神经元的GABA能输入。
